Comparison of Air Conditioning System (1)

8/17/2019 Comparison of Air Conditioning System (1)

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COMPARISON OF AIRCONDITIONING SYSTEM


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Air ConditioningSystem

Chilled Water Direct Expansion

Water-CooledChiller

Air-CooledChiller

Water-CooledPackaged

Air-CooledPackaged


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When selecting a cooling system, the firststep is to analyze commercial aspects andapplications of the systems to the job site.

There are a few criteria to considered whenselecting a cooling systemcapital costOperating cost

User’s ability to operateService and maintenance


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1) CAPITAL COST


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1) CAPITAL COST

WCChiller

ACChiller

WCPackaged

ACPackaged

System Price/ RT

RM 7000 TORM 8000

RM 5000TO RM 6000

RM 3500 TORM 4000

RM 3000 TORM 3500

i) Centralized chilled water system capital cost is higher compareto packaged system. However, capital cost is not the only criteriato justify which system to use. Other criteria should also take intoconsideration before any system is selected.

RT = Refrigerant Tonnage


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4) OPERATION COST


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4) OPERATION COST

WCChiller

ACChiller

WCPackaged

ACPackaged

Overall Efficiencykw/tr 0.9

i) Centralized chilled water system has a better overall efficiencydue to precise control of chillers, pump and valves operations inaccordance to the varying load. The capacity regulation of chilledwater system is stepless (continuous). Optimization of chiller plantefficiency can be done with chilled water system. Variable flow

systems and inverter driven chiller provide better energy efficiencyand optimization to the chiller plant operation.ii) Packaged system has poor overall efficiency due to poor controlof capacity as the compressor can not load/unload precisely andcontinuously. Compressor can only on/off, control of capacity arebased on steps.

1.5 1.1 1.1


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4) OPERATION COST

The Air Conditioning and Refrigerant Institute (ARI) has establisheda system in ARI standard 550/590 – 2003 for measuring the totalchiller performance over full and part load conditions. It defines asintegrated part load value (IPLV) as an excellent method ofcomparing equipment on an equal basis.

IPLV =0.01

A+

0.42

B

0.45

C

0.12

D+ +

1

A = kw/tr at 100% loadB = kw/tr at 75% load

C = kw/tr at 50% loadD = kw/tr at 25% load


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2) ADVANTAGES /DISADVANTAGES


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2) ADVANTAGES / DISADVANTAGES

WCChiller

ACChiller

WCPackaged

ACPackaged

1) DiversityFactor

Yes(0.8-0.9)

Yes(0.8-0.9) No No

i) Diversity factor can be applied to centralized chilled watersystem. This is because the chilled water plant can be sized for theinstanteous cooling load. Since, all loads do not peak at the sametime, centralized chilled water system is 10% to 20% smaller thanthe total of the individual units at its peak.

ii) Diversity factor cannot be applied to packaged unit due to thefact that each unit serves individual rooms. As a result, there is aredundancy in capacity as units are selected based individual peakloads.


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WCChiller

ACChiller

WCPackaged

ACPackaged

2) CapacityControl

Good Good

i) Centralized chilled water system has better capacity control andexcellent part load performance value (IPLV) as the compressor isable to load and unload according to the building load. Hence amore precise control on the temperature and relative humidity (RH)

of the room.ii) Packaged system has poor capacity control as the compressor isable to cut in/out. As a result, load fluctuation and inconsistency incapacity control makes it difficult to achieve continuous comfortlevel and precise temperature and humidity control.

Poor Poor


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WCChiller

ACChiller

WCPackaged

ACPackaged

Standby Yes Yes

i) Centralized chilled water system has standby chiller that will runin case of chiller failure. Using multiple compressors will alsofurther increase the standby (or redundancy) of the system.Multiple compressor chiller can be used to provide standby withpartial load in case space for chiller system not sufficient to fit instandby chiller.ii) Each package system has poor standby. In case of compressorfailure, the package system still can operate at part load. Nostandby package system is installed. But to overall building,because it consists of many package system, if one packagesystem fails, the other package system still operates normally and

not affected.

No No


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WCChiller

ACChiller

WCPackaged

ACPackaged

4) Life Span(Years)

15-20

i) Centralized chilled water system using screw compressor isdesigned for rugged and reliable operation with few moving parts,low speed operation and high quality bearing. Life span of screwcompressor is up to 20 years.

ii) Packaged system using scroll compressor is not as rugged andreliable as screw compressor. The life span is shorter due tofrequent start / stop of the compressor. Generally, scrollcompressors are expected to last 8 to 10 years only.

15-20 8-10 8-10


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WC Chiller

5) SpaceRequirement

i) WC Chiller & Pumps - Plant Roomii) Cooling Tower - Roof topiii) Make Up Water Tank - Roof top

iv) AHU – AHU Room

AC Chiller

5) SpaceRequirement

i) AC Chiller & Pumps – Roof topii) AHU – AHU Room

AHU – Air Handling Unit


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WC Packaged

5) SpaceRequirement

i) WC Packaged - AHU Roomii) Cooling Tower & Pumps- Roof topiii) Make Up Water Tank - Roof top

AC Packaged

5) SpaceRequirement

i) Outdoor Unit - Roof top / Building Wallii) Indoor Unit - AHU Room

AHU – Air Handling Unit


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WCChiller

ACChiller

WCPackaged

ACPackaged

6) DistanceLimitation

No No

i) Centralized chilled water system has no distance limitation.Chilled water and condenser water pumps are able to circulatechilled water and condenser water over a long distance.

ii) WC Packaged also has no distance limitation. The condenserwater pumps are able to circulate the condenser water over a longdistance.

No Yes

iii) AC Packaged has distance limitation. The distance betweenindoor and outdoor unit is limited by the length of refrigerant piping.To properly allocating the outdoor unit can be troublesome.


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WCChiller

ACChiller

WCPackaged

ACPackaged

7) PotentialHealth Hazard(Legionnaire disease)

Yes No

i) WC Chiller and WC Packaged can has potential health hazardas cooling tower are open to contamination. Warm water is apotential breeding ground for bacteria and microorganismsespecially legionnaires' disease.

Yes No

ii) AC Chiller and AC Packaged does not use cooling tower. Hencethere are no potential health hazard on legionnaires' disease.


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WCChiller

ACChiller

WCPackaged

ACPackaged

7) PotentialHealth Hazard(Refrigerant Leakage)

No No

i) Centralized chilled water system are does not have any potentialrefrigerant exposure to the occupants. Refrigerant is confinedwithin chillers only. Leaking in water piping can be easily detected.

Yes Yes

ii) Packaged system has potential refrigerant exposure to occupants.Refrigerant leakage is difficult to detect.


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WCChiller

ACChiller

WCPackaged

ACPackaged

8) Noise levelTreatment

Good

i) Centralized chilled water system noise level can be properlytreated within the chiller plant room.

ii) WC Packaged noise level is difficult to be treated as thecompressor is inside the indoor unit. To properly treated the noise

level can be costly.iii) AC Packaged noise level is also difficult to be treated as thecompressor is inside the outdoor unit. Since the outdoor unit isnormally scattered around the building to properly treated the noiselevel is very costly.

Good Poor Poor


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3) MAINTENANCE


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WCChiller

ACChiller

WCPackaged

ACPackaged

2) ChemicalTreatment Yes No Yes No

1) CondenserTube Cleaning Yes No Yes No

3) MAINTENANCE

i) WC Chiller and WC Packaged requires additional condensertube cleaning and chemical treatment which can add on

maintenance cost.


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Lower Entering AIR and WATER Temperatures

1) AIR COOLED CHILLER Chiller

kW/ton

CHWP

kW/ton

CT

kW/ton

CWP

kW/ton

Total

kW/ton

950F @ 100% FL 1.10 0.12 0 0 1.160

850F @ 75% FL 0.90 0.12 0 0 1.020

750F @ 50% FL 0.82 0.12 0 0 0.940

750F @ 25% FL 0.82 0.12 0 0 0.940

Integrated System kW per ton 0.974

2) WATER COOLED CHILLER ChillerkW/ton

CHWPkW/ton

CTkW/ton

CWPkW/ton

TotalkW/ton

870F @ 100% FL 0.62 0.12 0.05 0.08 0.870

83.5 0F @ 75% FL 0.71 0.12 0.05 0.08 0.960

800F @ 50% FL 0.85 0.12 0.05 0.08 1.100

800F @ 25% FL 1.25 0.12 0.05 0.08 1.500



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Lower Entering AIR and WATER Temperatures

1) AIR COOLED PACKAGED AC Packaged

kW/ton

CHWP

kW/ton

CT

kW/ton

CWP

kW/ton

Total

kW/ton

950F @ 100% FL 1.210 0 0 0 1.210

850F @ 75% FL 1.330 0 0 0 1.330

750F @ 50% FL 1.250 0 0 0 1.250

750F @ 25% FL 1.310 0 0 0 1.310


2) WATER COOLED PACKAGED WC PackagedkW/ton

CHWPkW/ton

CTkW/ton

CWPkW/ton

TotalkW/ton

870F @ 100% FL 0.780 0 0.05 0.08 0.910

83.5 0F @ 75% FL 0.960 0 0.05 0.08 1.090

800F @ 50% FL 0.980 0 0.05 0.08 1.110

800F @ 25% FL 1.250 0 0.05 0.08 1.380



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Comparison of Air Conditioning System (1)

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